Flange Gasket Types by Service: Choosing the Right Gasket Type for Flat Face Flanges

Many flange leaks start with a simple mismatch: the flange is correct, the bolts are correct, but the gasket material or gasket style is wrong for the service. Understanding flange gasket types by fluid, temperature and flange face helps buyers avoid premature leakage, gasket blowout and repeated shutdowns.

This article focuses on practical service compatibility and answers one frequent question from purchasing teams: what is the right gasket type for flat face flanges? In most cases, flat face flanges use a full-face gasket that covers the full flange face and includes bolt holes. The material, however, must still be selected according to the medium, pressure, temperature and flange material.

Service condition	Common gasket option	Why it is selected	Buyer warning
Water and low-pressure utility lines	EPDM, rubber or non-asbestos full-face gasket	Good compression and economical sealing	Confirm chemical additives and temperature.
Flat face flanges	Full-face gasket	Distributes bolt load across the entire face	A narrow ring gasket may overload some flat face flanges.
Oil and fuel service	NBR or suitable compressed sheet gasket	Better resistance to oil than many general elastomers	Do not assume EPDM is suitable for oil.
Chemical service	PTFE or filled PTFE gasket	Strong chemical resistance in many media	Check creep, temperature and bolt load requirements.
Steam or high temperature	Graphite or spiral wound gasket	Handles higher temperature than many soft elastomers	Confirm flange rating and controlled tightening procedure.
High pressure RTJ service	Metal ring gasket	Designed for RTJ grooves and high seating stress	Only for RTJ flanges with correct groove dimensions.

Start with the Flange Face

Before choosing gasket material, confirm the flange face. Flat face, raised face and RTJ flanges use different sealing concepts. A raised face flange concentrates gasket compression on the raised sealing area. An RTJ flange uses a machined groove and a metal ring gasket. A flat face flange depends on a gasket that works across the full flange face.

That is why the common gasket type for flat face flanges is a full-face gasket. It helps spread load over the full contact area, especially on cast iron, ductile iron, FRP, plastic-lined or low-pressure flanges where concentrated stress can damage the flange.

Full-Face Gaskets for Flat Face Flanges

A full-face gasket has the same general outside shape as the flange face and includes bolt holes. During assembly, the bolts pass through the gasket, and the gasket supports the area around the bolt circle as well as the inner sealing area. This is different from a ring gasket, which sits inside the bolt circle.

For flat face flange assemblies, the full-face design can improve load distribution and reduce bending stress. However, it does not remove the need for proper torque. Too much bolt load can still crush the gasket or damage the flange, while too little load can leave leak paths.

Flange Gasket Types by Structure

The main flange gasket types can be grouped by construction:

• Soft cut gaskets: made from rubber, PTFE, graphite sheet or compressed fiber sheet. Common in water, chemical and general service.
• Full-face gaskets: soft gaskets shaped to cover the full flat face flange and bolt holes.
• Ring gaskets: cut to fit raised face flanges inside the bolt circle.
• Spiral wound gaskets: metal winding with filler material, often used for pressure and temperature cycling.
• Metal jacketed gaskets: soft filler covered by a metal jacket for heat exchanger or special equipment service.
• RTJ metal gaskets: solid metal ring gaskets used with ring type joint flanges.

Material Compatibility Comes First

A gasket that seals well on day one can fail quickly if the medium attacks the material. EPDM can be a good choice for many water and steam-related applications, but it is not suitable for many oil services. NBR can suit some oil and fuel applications, but it has its own temperature and chemical limits. PTFE is widely used for chemical resistance, but it can creep if the joint design and bolt load are not suitable.

For stainless steel flanges in chemical or food-related service, buyers may also need to check cleaning chemicals, chloride exposure, FDA requirements, color coding, certificates and whether the gasket will be replaced during routine maintenance.

Temperature and Pressure Change the Decision

Temperature changes gasket behavior. Elastomers can harden, soften or lose recovery. PTFE can creep under load. Graphite performs well in many high-temperature duties but may not be ideal for every oxidizing environment. Spiral wound gaskets can perform well under cycling, but only when flange finish, bolt load and centering are correct.

Pressure also matters. A low-pressure water flange may seal with a soft full-face gasket. A higher pressure raised face flange may require a spiral wound gasket or other engineered solution. The flange class alone is not enough; the real operating pressure and temperature should be reviewed together.

Do Not Ignore Flange Material

Cast iron flat face flanges are often paired with full-face gaskets and controlled bolt tightening to reduce fracture risk. Carbon steel flanges can usually tolerate higher bolt loads, but corrosion around the gasket area should be checked. Stainless steel flanges need gasket materials that avoid contamination and suit the fluid environment.

If one side of the joint is flat face and the other side is raised face, stop and review the specification. Mismatched flange faces can create uneven gasket stress and mechanical damage.

Installation Checklist for Better Sealing

Check item	What to verify	Why it matters
Flange face	Flat face, raised face or RTJ	Determines gasket style and seating area
Gasket dimensions	ID, OD, bolt holes and thickness	Prevents blocked flow or poor bolt alignment
Material compatibility	Fluid, cleaning chemical and temperature	Prevents swelling, cracking or chemical attack
Bolt condition	Grade, length, threads and lubrication	Controls gasket compression
Tightening method	Cross pattern and staged torque	Improves even gasket stress
Reuse policy	New gasket after disassembly	Compressed gaskets often lose recovery

Procurement Notes for Export Orders

When ordering flanges and gaskets together, provide the flange standard, pressure class, face type, material, operating medium, temperature range and gasket style. For flat face flanges, clearly state whether a full-face gasket is required. For chemical, sanitary or marine projects, include documentation requirements such as material certificates, FDA statement, inspection report or packing requirements.

Songhai Flange can support industrial flange projects where flange face, gasket style and bolting requirements must work together. Providing the gasket information during flange inquiry can also help avoid a mismatch between flange finish and gasket material.

Erreurs courantes

• Using a ring gasket where a full-face gasket is required.
• Selecting gasket material by price without checking the medium.
• Reusing a gasket after disassembly.
• Ignoring temperature cycling and gasket relaxation.
• Mixing flat face and raised face flanges without engineering review.
• Applying excessive torque to fragile flat face flanges.

FAQ

What is the standard gasket type for flat face flanges?

The common gasket type for flat face flanges is a full-face gasket with bolt holes. It covers the full flange face and helps distribute the bolting load.

What are the most common flange gasket types?

Common flange gasket types include full-face gaskets, ring gaskets, spiral wound gaskets, PTFE gaskets, graphite gaskets, non-asbestos gaskets and metal RTJ gaskets.

Can PTFE gaskets be used on flat face flanges?

Yes, PTFE full-face gaskets can be used when chemical resistance is required, but pressure, temperature, creep resistance and bolt load should be reviewed.

Should flat face flanges use high torque?

Not automatically. Some flat face flanges can be damaged by excessive bolt load. Use the project procedure, flange material limits and gasket supplier guidance.

Final Thoughts

Choosing among flange gasket types is a service decision, not just a size decision. Start with the flange face, then check medium, pressure, temperature, flange material and assembly method. For the common gasket type for flat face flanges, a full-face gasket is usually the right starting point, but the final material must still match the real operating conditions.